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2015-06-29

New EVM rubber for reduced mixing times

  • Pre-crosslinked granules
  • Even easier to process
  • Ideal for continuous mixing processes

Specialty chemicals company LANXESS is launching a new family of pre-crosslinked EVM rubbers, in the form of the ethylene-vinyl acetate copolymers of the Levapren PXL series. These have been developed specifically for rapid processing in particularly cost-effective, continuous mixing processes – using Buss co-kneaders, for instance, or twin-screw extruders. Among other things, the free-flowing granules are ideal for reducing mixing times when producing particularly high-quality hoses or cable sheathings. Samples of the new ethylene vinyl acetate rubbers have already been made available to the first customers. The first grades to be available are 500 PXL, 600 PXL, 700 PXL and 800 PXL, with vinyl acetate contents of between 50 and 80 percent. The properties of vulcanizates produced using Levapren PXL are similar to those made using conventional EVM rubbers from LANXESS.

Processing advantages

“Standard Levapren grades have a much lower Mooney viscosity than many other synthetic rubbers,” says EVM specialist Jörg Stumbaum from the High Performance Elastomers business unit at LANXESS. “This brings several advantages – for instance, fewer plasticizers or even none at all are needed for EVM processing. However, some users require EVM rubbers with somewhat higher viscosity. For some time now, we have been able to offer these customers our pre-crosslinked Levapren XL grades.”

However, the technical conditions of the radiation crosslinking process used in the production of these grades mean they have to be mixed very well if the surface of the extrudates has to meet particularly high quality standards. “We have therefore long been looking for an alternative crosslinking technology, and have now found the solution in reactive extrusion,” says Stumbaum.

In this process, the polymer is pre-crosslinked with very small amounts of peroxide – although it is ensured that the product does not contain any traces of the crosslinking agent at a later stage. The process ensures that all Levapren PXL granules have the same crosslinking density. The result is free-flowing EVM granules that are quick and easy to process in an internal mixer or in continuous mixing processes and deliver exceptional flow properties – this is reflected, for example, in the particularly high surface quality of the extrudates. The rubbers in the Levapren PXL series also provide much higher green strength than standard and XL grades. “This can increase process reliability in the production of feeding strips for the extruder, for instance,” says Stumbaum. “And the increased creeping strength can also have benefits for hose and profile extrusion.” What’s more, the new Levapren PXL grades from LANXESS are much less susceptible to blocking even after long-term storage, which keeps the material free-flowing.

“Levapren PXL is a pre-crosslinked EVM grade that we have developed specifically for quick and cost-effective processing in continuous production. This technology is set to become increasingly important – and not just for SMEs in the rubber processing industry,” says Stumbaum. “We are also aiming to extend the user group to processors of rubber and plastics who have not been able to work with Levapren until now. Thanks to Levapren PXL, versatile EVM rubber has now become even more flexible.”

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LANXESS is a leading specialty chemicals company with sales of EUR 8.0 billion in 2014 and about 16,300 employees in 29 countries. The company is currently represented at 52 production sites worldwide. The core business of LANXESS is the development, manufacturing and marketing of plastics, rubber, intermediates and specialty chemicals. LANXESS is a member of the leading sustainability indices Dow Jones Sustainability Index (DJSI World and DJSI Europe) and FTSE4Good.

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